Method for continuous casting



pril 30, 19 s. R. MILLIKEN ET AL 3,087,213

METHOD FOR commuous CASTING Filed Nov. 25. 195'? I W W W Ni [5; r x I 1NH! so enter/P.

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ATTORNEY United States Patent 3,087,213 METHOD FOR CONTINUOUS CASTlNGSpencer R. Millikan, Lower Bnrrell Township, Westmoreland County, andEarl J. Schafer, Whitehall, Pa., as-

signors to Aluminum Company of America, Pittsburgh,

Pa., a corporation of Pennsylvania Filed Nov. 25, 1957, Ser. No. 698,5674 Claims. (Cl. 22-492) This invention relates to a method for thecontinuous and semi-continuous casting of ingots of aluminum base alloyscontaining 0.1 to 15 percent magnesium. In particular, it relates to amethod wherein the mold is provided with a lubricant containing anorganic BF carrier compound which will yield boron trifluoride vapors atelevated temperatures so as to provide about the metal ingot aprotective atmosphere which reduces or eliminates undesirable surfaceeifects such as heavy oxidation, tearing, cold shuts, or the like.

The term continuous," as herein used, refers to the progressive anduninterrupted formation of a cast body or ingot in a mold or die whichis open at both top and bottom. The pouring operation may continueindefinitely if the cast body is cut into sections of suitable lengthbelow the mold or the pouring operation may be started and stopped inmaking each ingot. In the latter case the process is often referred toas being semi-continuous.

For convenience, an aluminum base alloy containing 0.1 to 15 percentmagnesium, alone or in combination with other elements, will behereinafter referred to as an aluminum-magnesium alloy.

It is well-recognized that considerable difficulty is experienced in thecontinuous casting of aluminum-magnesium alloy ingots. The surface ofthe ingot is often heavily oxidized and marred by tearing, exudation,and other defects, all of which may result in an unacceptable ingot. Ithas been found that these surface defects are often attributable to theheavy oxidation of magnesium at the external surface of the ingot andthat the particles of these oxides of other oily-compounds act as focalpoints for further oxidation on and within the surface.

It is an object of this invention to provide a method for continuous andsemi-continuous casting of aluminummagnesium alloy ingots, wherein heavyoxide formation on the surface is greatly reduced, if not substantiallyeliminated.

It is also an object to provide a method for continuous andsemi-continuous casting of aluminum-magnesium alloy ingots, wherein coldshuts and tearing of the ingots are substantially eliminated.

It is a further object to provide a method for the continuous andsemi-continuous casting of aluminumrnagnesium alloy ingots wherein anoxidation-inhibiting film is 'formed on the surface of the ingot.

It has been discovered that the above objects, and others which willbecome evident herein, may be obtained by a method for continuous andsemi-continuous casting of aluminum-magnesium alloy ingots, wherein themold is lubricated with a grease or oil composition containing anorganic BF -carrier compound which will yield boron trilluoride at theelevated temperatures of the casting process. It has further been foundthat the boron trifiuoride content of the mold lubricant should bebetween 0.1 and 1.0 percent by Weight of the entire composition.

It has previously been determined that inorganic compounds such asammonium, potassium and sodium i'luoroborates in mold lubricants are noteffective oxidation inhibitors in the casting of alumium-magnesium alloy3,087,213 Patented Apr. 30, 1963 "ice ingots. Furthermore, the use ofsuch substances has generally been found to increase cold shuts andtearing.

The term aluminum-magnesium alloy," as herein employed, refers to analuminum base alloy containing 0.1 to 15 percent magnesium, with orwithout the presence of other elements, such as from 0.1 to 12 percentcopper, or 0.25 to 14 percent silicon or 0.1 to 20 percent zinc, or 0.1to 3 percent manganese, or combinations of two or more of theseelements. Any of the foregoing alloys may also contain one or more ofthe following elements, often referred to as hardeners, in the followingpercentages:

0.05 to 0.5 percent chromium 0.01 to 0.5 percent titanium 0.25 to 2.5percent nickel 0.01 to 0.5 percent boron 0.002 to 2 percent beryllium0.1 to 0.5 percent molybdenum 0.1 to 0.5 percent zirconium 0.1 to 0.5percent tantalum 0.1 to 0.5 percent columbium 0.1 to 0.5 percent cobaltHowever, the total amount of the latter elements should not exceed about3 percent.

The term organic BF -carrier compound, as used herein, refers to organiccompounds or complexes which will yield boron trifiuoride in a reactivestate at temperatures above 45 C. but below about 500 C. These carriercompounds are selected from the group consisting of R-HBF, and X-BFwhere R represents a nitrogencontaining organic compound having a basiccharacter such as an amine or amide, and where X represents an organicsubstance or carrier which will sorb or hold BF when treated therewith.

Generally, the R-HBF, compounds may be described as being the productsof reaction between the nitrogencontaining organic compound andhydrofluoroboric acid, HBF Those organic substances which contain sorbedor held B1 comprise a wide range of complexes, and in a few instancesperhaps compounds, which may be prepared in various ways but which, forthe most part, may be conveniently prepared by exposing the basematerial X to direct contact with gaseous B1 Whether these substances becompounds or complexes or a solution of B1 in the base material ormerely the undefined result or reaction product of the treatment with BFof a material which has an unsatisfied valence which will act as anacceptor of B1 they are, for the purposes of this invention, alike ifthey will yield BE; in a reactive state at the temperatures developed inthe casting mold.

The formula R-HBF may be described as the reaction product ofhydrofluoroboric acid, HBF.,, and an aliphatic carbocyclic orheterocyclic, mono or polyamine or hydroxy amine or amide, or analkaloid, or carbocyclic diazo compounds, or any other basicnitrogen-containing organic compound. Amines such as the following canbe used; butyl amine, di-n-butyl amine, amyl amine, ethylhexyl'amine,dodecyclamine, didodecyclamine, tetraethylamine, dioctadecyclamine,tetramethylamine, trihexylamine, ethylene diamine, diethylene triarnine,triethylene tetramine, di(2-ethylhexylarnine),N-phenyl-N,N,N-trimethylamine, tri-n-amyl amine, aniline, N-octadecyl-N,N,N-trimethylarnine, 3-phenyl propylamine, Z-pentyl-4,5-dimethyl-4-hexanooxyethyl 2 oxazoline, 2-pentyl-4, N-dodecylbenzylN,N,N trimethylamine, 4-bis(hexano oxymethyD-Z-oxazoline,2-nonyl-4-ethyl-4-caproxymethyl-2ethyl oxazoline, monoethanolamine,diethanolarnine, triethanolamine, aminoethanolamine,diethylarninoethanol, 3-di-n-amylaminopropylamine, monoisopropanolamine,phenyl ethanolamine, phenyl dicthanolamine,o-dimethylaminoethyl-p-octyl, phenol, 4-amino-3-pentadecyl phenol,nitron, phenyl morpholine, and l-hydroxyethylheptadecenyl lyoxalidine.Examples of amides which can be used are acetamide, propionamidc,butyramide, benzamide, cinnamide, nicotinamide, diacetamide,triacetamide, n-hexadecylamide and n-octadecylamide. Among the alkaloidswhich may be used are neurine, morphine, brucine, cocaine, and othersubstances employable are the diazo compounds formed from substancessuch as aniline, p tluoroaniline, nitroaniline, o-tluidine, xylidine andnaphthylamine.

The carrier or substance represented by X in the formula X-BF may beselected from a wide range of organic substances, among them being:ethylamine, diethylamine, phenyl-dimethylamine, acetonitrile, acetamide,aniline, pyridine, butyric acid, benzoic acid, trimethylamine oxide,diethyleneglycololeate, butyl stearate, acetamide, n-hexylether,morpholine, dioxane, urea, oleic acid, linoleic acid, lard oil, cetylalcohol, diethylenetriamine, oxazoline and tallow.

The formulae X-BF and R-HBF it should be understood, do not necessarilyimply an equimolecular ratio between X and BF or R and HBF but ratherthat the organic material may be associated with BF or H313, in anyproportion.

When either X-BF or R-HBF, is used, the carrier compound should be addedto the lubricant so as to provide between 0.1 and 1.0 percent by Weightof boron trifluoride in the total composition. Amounts of less thanabout 0.1 percent do not provide the benefits of this invention andamounts in excess of 1.0 percent are found to result in excessive vaporformation, tending to produce surface defects. Generally, it ispreferred to use a lubricant composition containing between 0.3 and 0.5percent by weight of boron trifluoride.

Generally, the lubricant is usually applied to the mold prior to thecommencement of casting by manually brushing or swabbing it onto themold surface. However, in some instances, especially in high-speedproduction lines, an automatic or semiautomatic feed system may beemployed by which the lubricant is initially applied and may be suppliedintermittently or continuously during the casting drop.

Referring to the attached drawing, diagrammatically illustrated is oneform of apparatus by which a liquid or semi-liquid lubricant may becontinuously or intermittently fed to the mold surfaces. Seated upon therectangular mold shell 2 is a lubricant feed device 4 having tubes orchannels 6 and outlets 8. Lubricant is supplied under pressure to thechannels 6 through feed lines 10 and is discharged through the outlets 8whence it spreads across the lip 12 and onto the walls of the mold 2.Due to its liquid or semi-liquid state, it flows downwardly along thewall to the interface between the mold and the ingot 14, and below.

Lubricant is desirably supplied at a low rate so that sudden chilling ofthe liquid metal meniscus is prevented. It is also desirable that thelubricant feed be prevented from impinging directly upon the surface ofthe molten metal, such as by use of a lip or other means which willdirect the flow onto the sides of the mold.

The mold lubricant to which the carrier substance is added may be of amineral, animal or vegetable base, or a combination thereof. Generally,however, lubricants must prevent wetting of the mold by the liquid metaland provide a lubricating film on the mold at all times. If oils areemployed, it is preferred that a continuous system of lubrication beemployed, especially in the casting of longer ingots, since the lighterhydrocarbon oils have a tendency to distill or carbonize. Greases orsemisolid hydrocarbon materials are conveniently employed because oftheir higher heat resistance and ability to provide a more durablelubricating film.

Generally, the conditions of casting determine the amount of lubricant,and also the degree of viscosity if continuous lubrication is employed;however, excessive amounts are undesirable because of flammability andcarbonization. Volatile liquid vehicles may be employed in the lubricantcomposition as an aid in application or transportation; however, thelubricating base itself should be relatively heat-stable, i.e., have afairly high boiling point and fairly high viscosity.

Combination of greases and oils have been satisfactorily employed, ashave been compositions containing various additives such as silicones,graphite, extreme pressure agents, etc. Generally, however, thelubricant base should comprise at least 50 percent of the totalcomposition.

Another aid often employed in the casting process is vibration of themold during the casting drop, which has been found of assistance inreducing tearing and cold shuts. If so desired, this vibration methodmay be used in combination with the method of the instant invention.

Illustrating the efiicacy of the present invention are the followingexamples wherein aluminum-magnesium alloys were cast by asemi-continuous process. Generally, in each case, the aluminum moldshells were brushed with a lubricant composition consisting of 1.0percent by weight of di-n-butylammonium tetrafiuoroborate in a standardmold grease (50 percent of lard-50 percent of calcium-lead base greasecontaining about 15 percent graphite). The metal pouring temperature wasbetween 1275 F. and 1300 F. and lowering rates of 2 /2 to 4 inches wereemployed. Water sprays were used to chill both ingot and mold.

Example 1. An alloy nominally composed of aluminum, 5.0 percentmagnesium, 0.1 percent manganese, 0.1 percent chromium and 0.15 percenttitanium was cast into extrusion ingots 8 inches and 14 inches indiameter, the mold lengths being 8% inches and 18 inches, respectively,and the molten metal heads being about '7 inches and 16 inches. Attemptsto cast this alloy by previous commercial practice, i.e., using astandard commercial lubricant containing no BF additive, resulted inacceptance of only 15 to 20 percent of the ingots due to severe tearingand cold shuts in addition to heavy oxidation. When the lubricantcontaining BF was employed, visual inspection of the ingots indicatedthat surface oxidation and exudation had been greatly reduced and thatcold shuts and tearing had been substantially eliminated, permittingacceptance of more than percent of the ingots.

Example 2.An alloy nominally composed of aluminum, 3.5 percent magnesiumand 0.25 percent chromium was cast into ingot 8 inches and 9 inches indiameter, the mold length being 8% inches and the molten metal headabout 7 inches. Standard practice had been unsatisfactory, allowing only17 to 25 percent acceptance. The ingots cast by the present methodexhibited only light oxidation and considerably reduced exudation;further, cold shuts and tearing were substantially eliminated, thuspermitting acceptance of more than 80 percent of the ingots.

Example 3.An alloy nominally composed of aluminum, 5.25 percentmagnesium, 0.8 percent manganese, 0.1 percent copper and 0.1 percentchromium was cast into ingots 8 inches and 9 inches in diameter, themold length being 8% inches and the metal head about 7 inches. Visualexamination revealed little oxidation and exudation and only rareinstances of cold shuts and tearing.

Example 4.An alloy nominally composed of aluminum, 1.0 percent magnesiumand 0.3 percent manganese was cast into ingots 9 inches and 11 inches indiameter, the mold lengths being 8% inches and 10 inches, respectively,and the molten metal heads about 7 inches and 8 inches. Upon visualexamination, exudation and oxidaton were found to be insignificant andcold shuts and tearing were noted to be substantially eliminated.

Having thus described the invention, we claim:

1. In the continuous and semi-continuous casting of aluminum base alloyingots containing 0.1 to 15 percent magnesium, the method wherein themold is lubricated with a composition containing an organic BF -carriercompound selected from the group consisting of R-HBF and X-BF where Rrepresents a basic nitrogen-containing organic compound and X representsan organic substance which will sorb or hold BF when treated therewith,said carrier compound decomposing at least in part to yieid borontrilluoride in an active state as it is heated to a temperature between45 and 500 C. during the casting process.

2. In the continuous and semi-continuous casting of aluminum base alloyingots containing 0.1 to 15 percent magnesium, the method wherein themold is lubricated with a composition containing an organic BF -carriercompound selected from the group consisting of R-HBF, and X-BF where Rrepresents a basic nitrogen-containing organic compound and X representsan organic substance which will sorb or hold BF; when treated therewith,and the BB, content being between 0.1 and 1.0 percent by weight of thetotal lubricant composition, said carrier compound decomposing at leastin part to yield boron trifiuoride in an active state as it is heated toa temperature between 45 and 500 C. during the casting process.

3. The method of claim 2 wherein the BF; content is between 0.3 and 0.5percent by weight of the total lubricant composition.

4. In the continuous and semi-continuous casting of ingots of aluminumbase alloys containing from 0.1 to 15 percent magnesium wherein the moldand emerging ingot are chilled by the direct application thereto of aliquid coolant, the method of substantially eliminating the occurrenceof cold shuts, tears and heavy oxide formation on the ingot surfacescomprising lubricating the mold with a composition containing an organicBP -carrier compound selected from the group consisting of R-HBF and X-BP where R represents an organic basic nitrogencontaining compound and Xrepresents an organic substance which will sorb or hold BF when treatedtherewith and the BF}, content being between 0.1 and 1.0 percent byweight of the total lubricant composition, said carrier compounddecomposing at least in part to yield boron trifluoride in an activestate as it is heated to a temperature between and 500 C.

References Cited in the file of this patent UNITED STATES PATENTS2,092,033 Stroup Sept. 7, 1937 2,135,183 Junghaus Nov. 1, 1938 2,137,715Erdrnann et al Nov. 22, 1938 2,380,202 Stroup July 10, 1945 2,611,743Kipp Sept. 23, 1952 2,747,244 Goss May 29, 1956 FOREIGN PATENTS 645,202Great Britain Oct. 25, 1950

1. IN THE CONTINUOUS AND SEMI-CONTINUOUS CASTING OF ALUMINUM BASE ALLOY INGOTS CONTAINING 0.1 TO 15 PERCENT MAGNESIUM, THE METHOD WHEREIN THE MOLD IS LUBRICATED WITH A COMPOSITION CONTAINING AN ORGANIC BF3-CARRIER COMPOUND SELECTED FROM THE GROUP CONSISTING OF R HBF4 